Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

Near field propagation law & a novel fundamental limit to antenna gain versus size

Abstract: The paper presents a theoretical analysis of the near field channel in free space The theoretical model is then validated by comparison to data measured in an open field The results are important for low frequency RF systems, such as those operating at short range in the AM broadcast band (525-1715 kHz) Finally, the paper establishes a novel fundamental limit for antenna gain versus size

Dispersion-enhanced photonic crystal fiber array for a true time-delay structured X-band phased array antenna

Abstract: Tunable optical true time-delay modules based on highly dispersive photonic crystal fibers (PCFs) are demonstrated to provide continuous radio-frequency squint-free beam scanning for an X-band (8-12 GHz) phased array antenna system. The dispersion of the fabricated PCF is as high as -600 ps/nm /spl middot/ km at 1550 nm. The time delay is continuously tunable from -31 to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far field radiation patterns of a 1/spl times/4 subarray were measured from -45/spl deg/ to 45/spl deg/ scanning angles. Squint-free operation is experimentally confirmed.

The determination of the surface impedance of a partially coated obstacle from far field data

Abstract: A variational method is given for determining the essential supremum of the surface impedance of a partiallycoated perfect conductor from a knowledge of the far field pattern of the time-harmonic electric field at fixed frequency. It is assumed that the shape of the scatterer has been determined (e.g., bysolving the far field equation and using the linear sampling method). Numerical examples are given for the scalar case with constant surface impedance.

Diffraction of electromagnetic wave by disk and circular hole in a perfectly conducting plane

Abstract: The scattering of electromagnetic plane wave by a perfectly conducting disk is formulated rigorously in a form of the dual integral equations (abbreviated as DIE). The unknowns are the induced surface current (or magnetic field) and the tangential components of the electric field on the disk. The solution for the surface current is expanded in terms of a set of functions which satisfy Maxwell's equation for the magnetic field on the disk and the required edge condition. At this step we have used the method of the Kobayashi potential and the vector Hankel transform. Applying the projection solves the rest of a pair of equations. Thus the problem reduces to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals with a single variable and these may be transformed into infinite series that are convenient for numerical computation. The numerical results are obtained for far field patterns, current densities induced on the disk, transmission coefficient through the circular aperture, and radar cross section. The results are compared with those obtained by other methods when they are available, and agreement among them is fairly well.